In recent years, as the digitalization of audio-visual apparatuses has progressed, copying is made possible without causing any deterioration in the quality of contents. However, copying copyrighted contents without limitation will result in infringing the rights of copyright holders. Audio-visual apparatuses are also requested to have an appropriate copyright protection function. Not only recording apparatuses but also reproducing apparatuses are requested to have a function that prohibits the reproduction of illegal contents.
As a copy control system for digital audio apparatuses, the serial copy management system (hereafter simply referred to as SCMS) has been used widely since 1980s. In the SCMS, copy control information is recorded, together with contents, on recording media, such as CDs and MDs, and media, such as airwaves, and copying possible/impossible control is carried out according to the copy control information of contents when the contents are copied inside the same housing of an apparatus or between different apparatuses connected via a digital interface. The SCMS has achieved a considerable effect on consumer-oriented recording apparatuses, such as MD players.
However, in the SCMS, copy control information is digital data independent of contents. Hence, when the contents are analog-transmitted according to the SCMS, the copy control information cannot be transmitted, and copy control cannot be carried out either. Furthermore, in the SCMS, there is a problem that the copy control information can be disabled easily using a personal computer or the like.
In consideration of this kind of problem encountered in the SCMS, the music industry, computer industry, consumer-oriented electronics industry, etc. gathered and established the SDMI (Secure Digital Music Initiative) standard. In this standard, a copy-control/reproduction-control system that uses digital watermarking technology is proposed.
A digital watermark is information embedded in a multimedia content, such as a still image, a moving image or audio data, so as not to be perceivable by human beings using the characteristics of the sensory perception of human beings, and is information different from the content itself. In other words, information different from the content is embedded in the content itself by adding a minor change unperceivable by human beings to the content. Digital watermarking is carried out using various methods, such as the echo control method, spectrum spread method, statistic operation method, phase operation method and static control method.
Even when a signal embedded with a digital watermark is reproduced, the difference from the original signal cannot be perceived by ordinary watching and listening, and the quality of the content is not impaired. Because the digital watermark is directly embedded in the content, copy control information can be transmitted even when analog transmission is used. In addition, the digital watermark has durability because the copy control information is retained even after the information is subjected to ordinary audio compression/decompression (MP3 or the like). Furthermore, the digital watermark cannot be read or written without using special embedding and deciphering apparatuses. Hence, copy control more powerful than the SCMS can be achieved by combining the digital watermark with the encipherment of the content itself.
As conventional reproduction control that uses digital watermarking, the reproduction control of the reproducing apparatus disclosed in Japanese Patent Application Laid-Open No. 2001-229612 is known. This publication describes a digital data copying control method and an optical disk reproducing method.
In the following description of the conventional reproduction control, the copy control information embedded in a content using digital watermarking is referred to as watermark CCI. On the other hand, the copy control information recorded on an optical disk as digital data independent of the content is referred to as digital CCI. In the reproduction from an optical disk, the digital CCI and the watermark CCI are requested to be subjected to reproduction control shown in FIG. 9. FIG. 9 is a table showing the details of the reproduction control for the attached information, that is, the digital CCI and the watermark CCI.
FIG. 10 is a block diagram of a conventional optical disk reproducing apparatus that uses the conventional copy control method. The conventional optical disk reproducing apparatus 174 shown in FIG. 10 is provided with a spindle motor 161 that rotates a disk 160, an optical pickup 162 that reads signals recorded on the disk 160, and a mechanism control section 163 that drives and controls the spindle motor 161 and the optical pickup 162. In the conventional optical disk reproducing apparatus, a signal processing section 164 takes data from the output of the optical pickup 162 and carries out error correction to extract a system stream, and outputs a control signal to the mechanism control section 163. A deciphering device 165 checks whether the system stream is enciphered or not, and deciphers the system stream if it is enciphered. A digital CCI decoding device 166 detects digital CCI from the unenciphered system stream that is output from the deciphering device 165. An AV decoding device 167 extracts a digital audio signal or a digital video signal from the unenciphered system stream that is output from the deciphering device 165, and decodes the signal. A watermark CCI decoding device 169 detects watermark CCI data from the digital audio signal or the digital video signal that is output from the AV decoding device 167. A D/A converter 168 converts the digital audio signal or the digital video signal into an analog audio signal or an analog video signal. A digital signal output control section 170 converts the digital audio signal or the digital video signal into a specified output format (for example, IEC60958 or IEEE1394), and controls the output of the converted signal. An analog signal output control section 171 controls the output of the analog audio signal or the analog video signal that is output from the D/A converter 168. A display section 172 displays the state of operation. A system control section 173 reads the watermark CCI data and the digital CCI data, and controls the digital signal output control section 170 and the analog signal output control section 171, and also controls the display section 172 and the mechanism control section 163.
The digital reproducing operation of the conventional optical disk reproducing apparatus 174 configured as described above will be described below.
In the digital reproducing operation, first, the signal recorded on the disk 160 is read using the optical pickup 162. While outputting a control signal to the mechanism control section 163, the signal processing section 164 takes data and carries out error correction to extract a system stream. The deciphering device 165 checks whether the system stream is enciphered or not, and deciphers the system stream if it is enciphered. The deciphering device 165 transfers the deciphered system stream and the unenciphered system stream to the digital CCI decoding device 166 and the AV decoding device 167. The AV decoding device 167 extracts a digital audio signal or a digital video signal from the system stream, decodes the extracted signal, and transfers the signal to the watermark CCI decoding device 169 and the digital signal output control section 170. The digital signal output control section 170 converts the digital audio signal or the digital video signal into a specified output format (for example, IEC60958 or IEEE1394), and outputs the converted signal. The digital CCI decoding device 166 decodes digital CCI data from the system stream, and transfers the data to the system control section 173. The watermark CCI decoding device 169 decodes watermark CCI data from the digital audio signal or the digital video signal, and transfers the data to the system control section 173. The system control section 173 reads the digital CCI data and the watermark CCI data, and controls the digital signal output control section 170 and the mechanism control section 163 according to the data. In addition, the system control section 173 transfers operation display information to the display section 172.
An example of a copy control flow during reproduction in the conventional optical disk reproducing apparatus configured as described above will be described below using FIG. 11.
First, a check is carried out as to whether the system stream output from the deciphering device 165 is enciphered or not (at step 1001). In the case that the system stream is enciphered, a check is carried out as to whether digital CCI data is present or not (at step 1002). In the case that digital CCI data is present, a check is carried out as to whether the digital CCI data is “copy-free” or not (at step 1003). As shown in FIG. 9, reproduction is permitted only when the digital CCI of the enciphered digital audio data or, digital video data is “copy-limited” or “copy-prohibited,” and reproduction is not permitted when the digital CCI is “copy-free.” Hence, in the case that the digital CCI data is “copy-free,” the disk is judged as a disk copied illegally. As a result, both the digital signal output control section 170 and the analog signal output control section 171 are controlled, and both the digital signal output and the analog signal output are muted (at step 1004). On the other hand, in the case that it is judged that the digital CCI data is not “copy-free” at step 1003, ordinary reproduction is carried out (at step 1008).
Furthermore, in the case that it is judged at step 1001 that the system stream is not enciphered and in the case that it is judged at step 1002 that there is no digital CCI data even if the system stream is enciphered, a check is carried out as to whether the watermark CCI obtained in the watermark CCI decoding device 169 is present or not (at step 1009). Next, in the case that watermark CCI data is present, a check is carried out as to whether the watermark CCI data is “copy-free” or not (at step 1010). As shown in FIG. 9, ordinary reproduction is made possible only when the watermark CCI data is “copy-free” (at step 1012). In other cases, that is, in the case that the watermark CCI data is “copy-limited” and in the case that the watermark CCI data is “copy-prohibited,” the disk is judged as a disk copied illegally. As a result, both the digital signal output control section 170 and the analog signal output control section 171 are controlled, and both the digital signal output and the analog signal output are muted (at step 1011).
A judgment is made as to whether the end of a reproduction unit (a piece of music or the like) is reached (at step 1005). If the end is not reached, the procedure returns to step 1001. If the end is reached, a judgment is made as to whether the end of the reproduction of the whole disk is reached or not (at step 1006). In the case that the end of the reproduction of the whole disk is not reached, the digital signal output control section 170 and the analog signal output control section 171 are reset to their ordinary output states (at step 1007), and the procedure returns to step 1001. On the other hand, when the end of the reproduction of the whole disk is reached, the reproduction is completed.
Patent document 1: Japanese Patent Application Laid-Open No. 2001-229612